This invention relates to electrical surge arresters. More particularly, it is concerned with electrical surge arresters for protecting electrical equipment having a large number of incoming lines from electrical transients caused by lightning or electromagnetic pulses on the lines.
It is frequently necessary to protect the electrical equipment of a communications system having a large number of incoming communication lines from electromagnetic pulses and lightning. Commonly, the equipment is placed in a shielded enclosure or shelter and a spark gap for shorting high voltage pulses to ground is provided on each incoming line at its point of entry into the equipment enclosure. In order to protect the equipment form an initial surge which might pass before the spark gap fires, a current limiting resistor and a low pass filter may be connected in each line, typically at the individual item of equipment to which the line is connected.
Although such arrangements are widely used for providing electrical surge protection, they do present some problems. In installations having a very large number of lines entering an equipment enclosure, close coupling between the lines leading into and out of a spark gap may have the effect of partially short-circuiting the spark gap protection reducing its effectiveness. Locating the spark gaps at the point of entry into the equipment enclosure and placing the additional protective elements within the individual items of equipment permits high voltage transients to enter the enclosure. These transients are difficult to control once they enter the enclosure and may be coupled to other wiring and be distributed throughout the equipment, causing either system malfunctions or damage.
Maintenance of a large number of lines and their associated spark gaps is difficult since the usual preventive maintenance entails visual inspection of each individual spark gap. Furthermore, since the spark gaps are located at the point of entry into the enclosure, removing and replacing one may temporarily violate the integrity of the electomagnetic shielding of the enclosure. In addition, conventional arrangement of spark gaps and associated protective elements require a considerable amount of space which increases in proportion to the number of lines which must be protected.